Our lab has focused on apoB mRNA editing as a model of post-transcriptional base modification in humans. ApoB mRNA editing is a site specific deamination of a cytidine residue to a uridine at nucleotide position 6666 in the ApoB mRNA transcript. The deamination reaction is a zinc dependent process mediated by a cytidine deaminase referred to as apolipoprotein B editing component 1 (APOBEC-1). RNA editing activity of AP0BEC-l is strictly dependent on assembly of an enzyme complex that includes APOBEC-l (the catalytic subunit), and auxiliary proteins. During the past year, we have examined regulation of apoB mRNA editing by analysis of post-transcriptional protein phosphorylation.